200 Nature's /IMractes. 



constructed with a very large number of con- 

 tacts made of metal sleeves, or tubes, say one 

 inch in diameter, so constructed that one will 

 slide within the other; the sleeves being slotted 

 so as to give them a little spring that secures 

 a firm contact. These are all connected to- 

 gether electrically, on each half of the switch, 

 as one conductor, so that when the switch is 

 closed the current is divided into as many 

 parts as there are points of contact in the 

 switch. Suppose there are 100 of these con- 

 tact-points, a one-hundredth part of the cur- 

 rent would be flowing through each one of 

 them. If, now, these points are so arranged 

 that they can be all simultaneously separated, 

 the spark that will occur at each break will be 

 very small as compared with what it would be 

 if the whole current were flowing through a 

 single point, and it would be so small that 

 there would be no danger attending the open- 

 ing of the switch. These switches are care- 

 fully guarded, being boxed in and under the 

 control of a single individual. 



There is another apparatus that is a neces- 

 sary part of every manufacturing or other 

 kind of plant that uses electricity from this 

 power-house, and this is called the transformer. 

 Many of you are familiar with the box-shaped 

 apparatus that is used in connection with 

 electric lighting when the alternating current 

 is used. Where simply heating effects are re- 



